1. Technical Field
This disclosure relates to charge of a rechargeable battery, and more particularly to a pulse modulation charging method and a pulse modulation charging apparatus, capable of charging a battery capacity close to saturation.
2. Related Art
Considering the charge requirement of a rechargeable battery, a charging method in the prior art uses a continuous and fixed current output to charge the rechargeable battery. However, continuously charging the rechargeable battery with a fixed current is likely to cause a polarization effect of battery electrodes, thereby forming impedance against a charge current and reducing charge efficiency.
In view of the above problems, many solutions are provided. For example, in U.S. Pat. No. 5,726,551 and U.S. Pat. No. 4,746,852, the continuous and fixed current output is modified to a pulse current output, so as to reduce the polarization effect of the electrodes. In Taiwan (R.O.C) Invention Patent No. 1285451 and Taiwan (R.O.C) Utility Model Patent No. M367511, a discharge pulse is further added into the pulse current, so as to interfere crystallization of ions around the electrodes, thereby reinforcing an effect eliminating the polarization effect of the electrode.
The polarization effect affects the charge efficiency, and in addition, a battery capacity of the battery also changes the impedance against the charge current. Especially when the battery capacity is close to saturation, the impedance of the battery against the charge current is also increased. When the battery capacity exceeds a certain degree, a rate of the charge current is reduced significantly, and charge efficiency suddenly reduces sharply as a result. Consequently, if the battery capacity needs to be charged close to saturation, a charging operation takes a long time. Generally, a fast charge fails to charge the battery capacity close to saturation; instead, some of the battery capacity is sacrificed.